Despite decades of research, the prognosis of most of the 17,500 patients diagnosed annually with brain cancer is very poor. The mortality rate of brain cancer patients is about 80 percent, second only to lung cancer patients whose mortality rate is about 85 percent (Bethune et al., Pharm. Res. 16(6): 896-905 (1999)). The standard treatment is surgical excision and radiation therapy with or without adjuvant chemotherapy. Unfortunately, the Food and Drug Administration has not approved many new drugs for treatment of brain cancer over the last three decades. As of 1997, carmustine (“BCNU”), lomustine (“CCNU”), procarbazine, and vincristine were still the most commonly used drugs for both newly diagnosed and recurrent gliomas (Prados et al., Sem. Surgical Oncol. 14: 88-95 (1998)). The use of adjuvant chemotherapy is currently controversial because very few patient respond to the standard chemotherapeutic protocols (Mason et al., J. Clin. Oncol. 15(12): 3423-3427 (1997)), although assays have been developed to identify which patients are likely to respond to chemotherapies. While these assays have improved survival rates slightly, the responsive tumors are in the minority and mortality rates remain high.
Numerous experimental trials have been attempted over the years with limited success. The most successful protocols (i.e., those that progressed to phase II clinical trials) involved combination therapies. The majority of single therapies did not pass phase I trials. Molecules such as the prototypical isoquinoline PX1195, benzodiazepine R0-4864, and the recently reported pyrrolobenzoxazepine NF 182 (Zisterer et al., Biochem. Pharmacol. 55:397-403 (1998)) form a class of agents that bind to the peripheral benzodiazepine receptors (“PBR”) and possess antiproliferative activity toward C6 glioma cells. The EC50 values for these agents are 73 μM, 95 μM, and 37.5 μM, respectively. While these PBR ligands have been useful as brain cancer imaging agents (Olsen et al., Cancer Res. 48:5837-5841 (1988)), they have not been demonstrated to be useful for treating cancer. Thus, a need exists to identify compounds having improved antiproliferative/cytotoxic activity on brain and/or other forms of cancer.
The present invention is directed to overcoming these and other deficiencies in the art.